Armat studied at the Mechanics Institute in Richmond, Virginia and then in 1894 at the Bliss Electrical School in Washington, D.C., where he met Charles Francis Jenkins. The two classmates teamed up to develop a movie projector using a new kind of intermittent motion mechanism, a "beater mechanism" similar to the one patented 1893 by Georges Demenÿ in France. It was one of the first projectors using what is known as the Latham loop (an extra loop of the film before the transport mechanism to reduce the tension on the film and avoid film breakage, developed independently at the same time by Woodville Latham and his sons). They made their first public projection using their invention, named Phantascope after an earlier model designed by Jenkins alone, in September 1895 at the Cotton States Exposition in Atlanta.

Following this success, the two co-inventors broke up over patent issues. Jenkins tried to claim sole inventorship, but was turned down and sold out to Armat, who subsequently joined and sold the patent to Thomas Edison, who marketed the machine as the 'Vitascope'. The projector was used in a public screening in New York City beginning April 23, 1896 and lasting more than a week.